1. Field of the Invention
The present invention relates to a wire saw machine for sawing an article to be processed, hereinafter referred to a work simply, e.g., a brittle material such as a semiconductor single crystal, a magnetic material, quartz, ceramic or the like, into a plurality of slices, and in particular, to an improved structure of a roller having grooves for the wire saw machine in which a cutting wire is wrapped around a plurality of rollers.
2. Description of Related Art
Conventionally, in order to manufacture a plurality of slices of a brittle material such as semiconductor wafers by cutting a work, a wire saw machine has been used. In the wire saw machine, semiconductor wafers or the like are manufactured by a lapping function to cut the work, that is, by pushing the work against a plurality parallel lines of cutting wire with a constant pitch, and by supplying an abrasive slurry containing abrasive grains into between the work and the lines of wire, while complex action of the cutting wire which comprises back and forth action and feeding action, is taken.
Although such a kind of wire saw machine has the disadvantage of a smaller speed for cutting a work than that of an inner diameter saw slicing machine, the wire saw machine has the advantage of simultaneous cutting of many wafers. For example, a cutting for a silicon single crystal having a diameter of 125 mm according to the wire saw machine requires about 6 hours, on the other hand, it enables obtaining about 200 cut wafers at a time.
In use of the wire saw machine, heat is generated by the friction between the lines of the cutting wire and the work and by the friction in bearing portions of the rollers with grooves thereof around which the cutting wire is wrapped, during cutting. Such generated heat changes the temperature of each roller with grooves during cutting to change the pitches of the grooves which are curved on the peripheral surface of each roller. Change of the pitches of the grooves on the periphery of the roller leads to change of the pitches of the lines of the cutting wire, during cutting. Consequently, undulations may be formed on the cut surfaces of the wafers or the like.
Conventionally, in order to solve the above-described problem, a rolling apparatus was developed, as shown in Japanese Patent Application Laid-Open Publication No. Tokukai-Sho 62-251063. The roller with grooves used in the rolling apparatus shown in the Publication has a cavity formed in a core member thereof, which constitutes a part of an oil passage. In the rolling apparatus, a cooling oil is introduced into the cavity through one end of the apparatus and is discharged from the other end.
However, the rolling apparatus in which a cooling oil is introduced into the cavity through one end of the apparatus and is discharged from the other end, raises the following problems.
Because the cooling oil which was supplied from an inlet for supplying oil into the cavity endothermically moves toward an outlet for discharging oil which is provided at the other end of the apparatus, the temperature of the oil becomes higher as the oil gets nearer to the outlet, so that the endothermic coefficient or the endothermic amount of the cooling oil becomes smaller. The difference between the endothermic amounts of the cooling oil at both ends generates a temperature gradient along the longitudinal direction of the rolling apparatus with grooves, and thereby pitches of the grooves for accepting the lines of wire, one by one, which are formed on the peripheral surface of a sleeve of the apparatus, are changed. Such tendency becomes larger, as the diameter or the length of the work such as a silicon single crystal ingot is larger. Conventional wire saw machines were used for cutting works having a diameter of about 150 mm and a length of about 300 mm. However, recently, cutting of larger works, e.g., having a diameter of about 200 mm and a length of about 800 mm to 1000 mm, is required.